According to conventional technologies, the following method has been used as a laser marking method of wafer dies. First, the back surface of a wafer in which wafer dies are integrated is made to have a desired thickness through backgrinding, and then, two wafer dies are selected as first and second reference wafer dies among wafer dies on the front surface of the wafer. By using the thus-selected first and second reference wafer dies, positions of all the rest wafer dies are identified and then, by using thus-identified position information, each wafer die is marked with a laser. Then, by dicing the wafer, the marked wafer dies are divided. However in this method, in the wafer dicing process fragments or chippings may be generated from the back surface of the wafer or the wafer may be damaged.
There is a dicing before grinding (DBG) process as a method to solve this problem. In the DBG process, a wafer in which wafer dies are integrated is half-cut before grinding, and then backgrinding is performed to divide wafer dies. Then, a marking process for the thus-divided wafer dies is performed with a laser. However, as the divided wafer dies are located askew from the original positions on the wafer, it is difficult to mark the wafer dies on an accurate position of each of the divided wafer dies with the conventional marking method using the two wafer dies, namely, the first and second reference wafer dies, for marking the rest wafer dies.
Meanwhile, a method of identifying position information of wafer dies by using a vision camera has been used according to conventional technologies. However, in this method, the vision camera photographs each wafer die individually to measure the position, and therefore the vision camera should perform the measuring job the same number of times as the number of the wafer dies. For example, if 1000 wafer dies are on a wafer, the vision camera should be used 1000 times to identify the position information of all wafer dies. Accordingly, it takes a long time.